Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.71   3.621%   $254.6072   $254.61   $254.60   $254.60  
  Purchase #2 $183.92   9.156%   $200.7597   $200.76   $200.75   $200.80  
  Purchase #3 $60.89   9.113%   $66.4389   $66.44   $66.45   $66.40  
  Purchase #4 $14.35   10.376%   $15.839   $15.84   $15.85   $15.80  
  Purchase #5 $46.97   5.572%   $49.5872   $49.59   $49.60   $49.60  
  Purchase #6 $24.83   7.226%   $26.6242   $26.62   $26.60   $26.60  
  Purchase #7 $75.31   5.650%   $79.565   $79.57   $79.55   $79.60  
  7 purchase totals = $651.98       $693.4212   $693.43   $693.40   $693.40